NASA's Mars Rover Opportunity has arrived at the rim of a crater approximately five times wider than a previous stadium-sized one it studied for half a year.

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Initial images from the rover's first overlook after a 21-month journey to "Victoria Crater" show rugged walls with layers of exposed rock and a floor blanketed with dunes. The far wall is approximately one-half mile from the rover.

"This is a geologist's dream come true," said Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for NASA's twin rovers Opportunity and Spirit. "Those layers of rock, if we can get to them, will tell us new stories about the environmental conditions long ago. We especially want to learn whether the wet era that we found recorded in the rocks closer to the landing site extended farther back in time. The way to find that out is to go deeper, and Victoria may let us do that."

Opportunity has been exploring Mars since January 2004, more than 10 times longer than its original prime mission of three months. It has driven more than 5.7 miles. Most of that was to get from "Endurance" crater to Victoria, across a flat plain pocked with smaller craters and strewn with sand ripples. Frequent stops to examine intriguing rocks interrupted the journey, and one large sand ripple kept the rover trapped for more than five weeks.

"We're so proud of Opportunity, the rover that 'takes a lickin' but keeps on tickin'," said Cindy Oda, a Mars rover mission manager at NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif. "It continues to overcome all challenges despite its aging parts and difficult terrain. We are looking forward to exciting new discoveries as Opportunity begins its new adventure exploring Victoria crater."

Spirit, halfway around Mars and farther south of the planet's equator, has been staying at one northward-tilted position through the southern Mars winter for a maximum energy supply for its solar panels. Spirit is conducting studies that benefit from staying in one place, such as monitoring effects of wind on dust. It will begin driving again when the Martian spring increases the amount of solar power available.

Operations for both rovers will be minimized for much of October as Mars passes nearly behind the sun from Earth's perspective, making radio communication more difficult than usual.

JPL manages the Mars Exploration Rover Project for the NASA Science Mission Directorate, Washington.